package com.samxcode.leetcode;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * Given a collection of candidate numbers (C) and a target number (T), find all unique combinations
 * in C where the candidate numbers sums to T.
 * 
 * Each number in C may only be used once in the combination.
 * 
 * Note: All numbers (including target) will be positive integers. Elements in a combination (a1,
 * a2, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤ ak). The solution set must not
 * contain duplicate combinations. For example, given candidate set 10,1,2,7,6,1,5 and target 8, A
 * solution set is: [1, 7] [1, 2, 5] [2, 6] [1, 1, 6]
 * 
 * solution:
 * similar to combination sum
 * 
 * @author Sam
 *
 */
public class CombinationSum2 {

    public List<List<Integer>> combinationSum2(int[] candidates, int target) {
        List<List<Integer>> res = new ArrayList<List<Integer>>();
        if (candidates == null || candidates.length == 0) {
            return res;
        }
        Arrays.sort(candidates);
        helper(candidates, res, 0, target, new ArrayList<Integer>());
        return res;
    }

    private void helper(int[] candidates, List<List<Integer>> res, int start, int target,
            ArrayList<Integer> path) {
        if (target == 0) {
            res.add(new ArrayList<>(path));
            return;
        }
        for (int i = start; i < candidates.length && candidates[i] <= target; i++) {
            //skip the repeat in the res
            if (i == start || candidates[i] != candidates[i - 1]) {              
                path.add(candidates[i]);
                //start=i+1
                helper(candidates, res, i + 1, target - candidates[i], path);
                path.remove(path.size() - 1);
            }
        }
    }
}
